1. Field of the Invention
The present invention relates to an optical packet header identifier for verifying whether or not an optical address code added to an optical packet signal transmitted from outside coincides with an address code previously given to an optical packet receiver without photoelectric conversion while maintaining the added code in the form of light and for outputting a result of the coincidence of codes as an electrical signal output in the event the two codes coincide with one another, an optical router incorporating the identifier therein, and an optical routing method using the optical router.
2. Description of the Related Prior Art
Advent of the Internet community has been drastically increasing communication traffic. Therefore, there is a demand for realization of a network that is able to accept the increase in communication traffic, have a high-capacity, operate at higher rate, and have at lower communication cost. Optical fiber communication technology is very the one that meets such requirements.
When focusing attention on the field of communication protocol, a connectionless communication typified by Internet Protocol (IP) is becoming increasingly dominant over a circuit switching connection typified by a telephone network. To achieve a high-capacity and high-speed communication system of the type used for connectionless communication, it is desirable to be able to perform optical signal transmission throughout from a transmitting terminal to a receiving terminal without any photoelectric conversion.
Routing is a technique for selecting an optimal path to be used from a plurality of communication paths in order to transmit an IP packet to a final destination. In an optical communication system, a wavelength routing system that employs a wavelength as address information to determine the destination of signal light has been known as a routing technique that uses an optical signal as it is. However, this routing technique can be applied only to a high-speed/capacity portion of communication network because a wavelength resource, i. e., the number of wavelengths to be allocated to individual addresses is limited. Currently, it is difficult to deliver an IP packet to an access path that needs a number of addresses while maintaining the packet in the form of light.
A technique using an optically encoding/decoding device for encoding a light signal, and in turn, decoding the encoded light signal is disclosed in Japanese Patent Application Laid-open No. 2001-177565.
FIG. 1 is the exemplary configuration of an optical encoder (note that the optical encoder can be used not only for encoding a light signal but for decoding the same) composed of 8-tip optical bipolar encoder of the type used in PLC (Planar Lightwave Circuit) in the above-described patent. A light pulse input to the optical encoder is branched into eight tip pulses that are made to have a time delay of 5 ps between adjacent pulses and equal intensity by operating a tunable optical tap 41 and an optical delay line 42. Each of the branched tip pulses is processed such that a phase shift “0” or “π” due to a thermal-optical effect by an optical phase shifter 43 is given to the optical phase of the tip pulse ,and then encoded by again combining the tip pulses together through a combiner 44. The given combination of phase shifts thus corresponds to one code. Each of the optical phase shifters 43 is controlled in response to an address code, thereby producing a desired optical bipolar code. In turn, when the optical bipolar code is input to the same optical encoder, a correlation between the optical code input thereto and the combination of phase shifts of the optical phase shifter is detected. A correlation signal having high intensity is output only when the optical code input thereto and the combination of phase shifts of the optical phase shifter coincide with one another, whereby the code is identified.
In the above-described optical encoder employed in the disclosed technique, since encoding or decoding is performed by giving a phase shift “0” or “π” to an electric field of light, the encoding or decoding is so sensitive to change in optical frequency. Furthermore, the optical encoder is not practical for use because it has no compatibility with the current optical fiber communication system in which data or address is transmitted/received by modulating the intensity of light.